Basic Home-Built Dye Laser Information

Dye lasers are unique in that they are a class of lasers whose lasing medium
is a liquid. Depending on the particular dye used, output can be at a wide
range of wavelengths spanning the visible spectrum and beyond.

Commercial dye lasers are often pumped by other lasers. For example,
Rhodamine-B, a common dye used in dye lasers for the red region, is often
pumped with an argon ion laser at 514 nm for CW operation or a doubled YAG
laser at 532 nm when pulsed. A suitable flashlamp can also be used as a pump
source (but not just any old electronic flash - it needs to be very intense
with a fast rise-time). As it turns out, this can easily be home-made.

In fact, the overall construction of a flashlamp pumped dye laser is quite
simple and straightforward, at least compared to nearly all of the other lasers
discussed in this chapter. At most, a minimal vacuum system is required (for
the home-made flashlamp) and there is absolutely no special glass work or need
for exotic gases (though finding the highly pure dyes may require a little
finger-work).

The hazards are also relatively moderate - some of the organic dye materials
are toxic and a high voltage power supply (low current but a BIG energy
storage capacitor) is needed to fire the flashlamp.

There are three areas of safety considerations for the home-built HeHg laser
(and other similar lasers, for that matter):

Laser output: The home-built Dye laser may be capable of producing
a pulses of coherent light with enough energy to be a hazard to vision.
Since there doesn't seem to be any hard information on the actual power or
energy obtainable with this or similar home-built laser designs, it is
important to take precautions assuming a higher power until determined
otherwise.

Avoid eye contact with the direct or reflected beam.

Electrical: The power supplies can be lethal. Neon sign transformer
based power supplies have enough voltage and current to stop a heart, The
charged energy storage capacitor for the flashlamp can be truly deadly. Even
if you aren't killed, the shock may startle you into doing something you might
regret. Make sure you read and follow the Safety
Guidelines for High Voltage and/or Line Powered Equipment. Insulate all
connections and install barriers to prevent contact with the high voltage.

Chemicals: Many laser dyes are toxic. Their solvents may be both
toxic and flammable. Take appropriate precautions in use and dispose of these
hazardous materials in a responsible way.

Provide proper warning signs for both the laser radiation and high voltage.
Keep pets and small children out of the area and make sure everyone present is
instructed as to the dangers. The use of proper laser safety goggles for the
specific wavelength(s) of your laser are highly recommended.

In addition to the article in: "Light and its Uses", there is also a fine
article on the operation of organic dye lasers in the February 1969 issue of
Scientific American. (This also happens to be the same issue that features
plans for the home-built argon ion laser.). The following should also be
of interest:

Puls Laser (German)
has virtually all of the home-built laser types including
CO2, N2 (including TEA), ion, ruby, dye, and some that aren't covered here.
It includes descriptions, photos, references, and other
information. An English translation would be most welcome as Altavista
does less than a stellar job and doesn't follow the frame links.

Information Unlimited has
plans for a tunable dye laser which is nearly identical to the one in
Scientific American. (The major difference I saw is that the air flashlamp
is pulse triggered rather than firing when the pressure is reduced by
allowing it to pump down). However, the somewhat more detailed instructions
in these plans (compared to the SciAm article), the availability of the
electronic parts (from Information Unlimited), and the list of suggested
companies to purchase the mechanical parts and laser dyes, may make them
beneficial to someone who isn't enthusiastic about scrounging, designing, or
improvising, and would rather take more of a cookbook approach to home-built
lasers. MWK Laser Products has plans
for the dye laser as well which I assume are similar but don't know for sure.

Exciton, a major manufacturer of
laser dyes has a very nice four-color laser wavelength chart,
an essential reference for your lab or office wall. They used to offer it
for free, though I applied twice and never received anything. The
chart can be displayed but can't be saved as a .gif or .jpg. I don't know
if they will sell it or give it away.

The dye laser can be constructed without any requiring any glass working, and
only a minimal vacuum capability (none if you use a commercial xenon flashlamp
instead of the home-built variety). However, the power supply can be lethal
and of course, liquids and HV do not mix!

Cooling - Flowing dye solution. Either a siphon or small pump can be
used.

Coupling - Quartz windows perpendicular to tube axis (tube end caps).

Mirrors - Aluminum coated, planar. HR: Fully reflective, actually 92%
reflected, 8 percent absorbed); OC: 74% reflective, 18% transmitted, 8%
absorbed. Dielectric mirrors would be more efficient but would be narrow
band requiring different mirrors for each substantial change in the color
of the dye/light. Three screw Adjustable Mirror
Mount at each end. Alignment technique not stated - can use any of the
techniques from this document or "Light and its Uses".

Total resonator length (mirror to mirror) - 120 mm.

Vacuum system (for home-made flashlamp):

Requirements - Low to medium. Must be able to pump down to a few Torr.
A salvaged refrigeration compressor should be adequate. See note below for
actual calculations of required vacuum. (None if a commercial xenon flash
lamp is substituted for the home-made variety.)

Power supply (for flashlamp) - Pulsed discharge from 15 uF, 5 kV low
inductance low ESR energy storage capacitor mounted in close proximity to
the flashlamp. Circuit shown is a simple
charger using a high voltage transformer and HV bridge rectifier. The
flashlamp is fired by pumping the air from it until the capacitor
discharges (about 60 Torr according to the article but see note, below).

Basically what is needed is a source of several thousand volts at low current
to charge the energy storage capacitor. There are many ways to get this.
An oscilloscope high voltage transformer would probably be quite difficult
to locate nowadays. Alternatives include: neon sign or oil burner ignition
transformer, high frequency high voltage inverter, lower voltage transformer
or inverter with voltage multiplier, and HeNe laser power supply.

An optional pulse generator can be used with an external trigger electrode
as well with the flashlamp running a a higher pressure.

Using a 15 uF, 5 kV capacitor without any inductor would likely cause
catastrophic failure at the first attempt to fire the xenon flashlamp. An
inductor would save the lamp but cause a great lengthening of the pulse
width which would not produce the needed flux density to excite the dye
to laser threshold. There are methods sometimes used to enable one to
utilize xenon flashlamps but these employ very high overvoltages (typically
.3 uF at 20 kV for this size lamp) and triggered spark gaps for firing.
This will usually keep the risetime of the lamp fast enough for success.

These set of guidelines should be followed during construction of your first
home-built dye laser. The factors below will greatly influence the
ultimate output power, beam quality, and whether it produces any coherent
light at all! Once you have a working laser, feel free to make
modifications - one at a time.

Pump the dye laser with either the air flashlamp or your nitrogen laser
(you have already built that, correct?). Disposable camera flash units
or even large studio strobes won't work due to their excessively
long flash duration. You can experiment with alternative pump sources once
you have a working laser.

Don't omit the dye circulating pump. Without fresh dye solution, the
number of shots before lasing dies out will be quite limited.

Although you are welcome to try virtually any colored compound in your laser
chamber to see if it will lase, sticking with what is known to work (at least
in the beginning) is probably the wisest choice. In that regard, the
following advice probably applies in general to dyes other than the one
mentioned:

(From: Chris Chagaris (pyro@grolen.com).)

Fluorescein (Uranin) or more specifically disodium fluorescein can be
purchased from a number of chemical houses. If you plan to use this compound
in a dye laser, it must be of a very pure grade. If this is the case, I would
suggest that you purchase it from one of the companies who specialize in
laser dyes such as Lambda Physik
at 1-800-EXCIMER, or Exciton at
1-937-252-2989. This is one of the least expensive laser dyes that can be
purchased and has good efficiency in the green wavelengths.

Conditions being what they are these days, an individual
can't generally buy things from a chemical company. While
it is possible to find Fluorescein on eBay (and also some
scintillators -- my first UV dye laser was PPO that I got
on eBay, pumped with a nitrogen laser), you can't just go
there and expect to find a gram of laser-grade R6G.

"Highlight" fluorescent markers. I've lased 2 or 3 of
the available colors. The Sharpie "Accent" yellow-barrel
marker (makes a yellow-green highlight) is probably the
best I've found so far.

Several of the brighteners used in laundry detergents
are good blue or indigo laser dyes. It is possible to use
some liquid laundry detergents directly. I lased All
“Free Clear” in 2000, using a low-pressure
nitrogen laser; and Jarrod Kinsey has recently been
getting very nice results with Arm and Hammer 2x liquid
concentrate, pumping it with a TEA nitrogen laser.

If you try this, remember to use detergents that are
listed as “No Dyes, No Perfumes”, and are as
close to water-clear as possible: murky blue gunk is
obviously not going to work. A few of the better organic
detergents actually are free of dyes, including
optical brighteners, so it’s a good idea to test
for fluorescence before you buy, or look for the word
“brightener” in the ingredient list. OTOH,
most or all of the major brands, at least the ones that
are transparent, appear to be good candidates.

You can, alternatively, make an alcohol extract of a dry
powder detergent (I have gotten my best results with Arm
and Hammer). This works extremely well, provided you can
filter or centrifuge the extract to remove the remaining
dusty bits of detergent. I believe that this method works
best with 91% pure (or higher) isopropyl alcohol or 95%
ethanol, but it may be possible to do it with 70% isopropyl
rubbing alcohol.

Far and away, however, the best thing I've found along
these lines so far is
“Optic
Whitener”, from Dharma Trading Co.
A very small amount of this, diluted with isopropyl
alcohol (70% rubbing alcohol from the drugstore seems to be
just about ideal) or ethanol, will fill a dye cuvette that
is pumped by a nitrogen laser; and the bottle contains 8
ounces, so it will last several lifetimes. I have also lased
this stuff in the "Minimalist" flashlamp-pumped dye laser
that I mention below, which stores only a dozen joules in
its capacitor bank.

I mention all of this because Jarrod, in an email message,
pointed out that these things should be really well known,
because people need the info, but they aren't  they
seem to be hiding under everybody's radar. I thought
it would be a good idea to alert you, because you are a
major hub of information for DIY people.

I should note, btw, that I have been getting 99+% iso at a
local electronics supply house. It is somewhat expensive,
but it works extremely well.

The SciAm/Lankard dye laser design is indeed a worthwhile project for a
hobbyist. Its specifications, optical requirements, and adjustments are far
less demanding than most of the other SciAm lasers. Plus, the design lends
itself to experimentation with a variety of modifications. The output is
extremely powerful. (While adjusting mine for peak power, it generated a beam
of sufficient intensity to vaporize the aluminum coating on my less than
perfect cavity mirrors.) Most of the parts are available from North Country
Scientific, RFD1, Plymouth, NH 03264. (I recommend all their parts EXCEPT
the mirrors.) The most costly part will be the capacitor. Condenser Product
in Florida can make one. Do not go over 15 to 20 uF or flashlamps will
shatter. Also, do not substitute anything else for the quartz parts. I also
recommend the electronic trigger circuit. Use only ultra pure solvents
(i.e., distilled in glass methanol). Dyes are available from Exciton Corp in
Dayton, OH. Also, read the sections describing the modifications to this
laser that other people have made. When I get back to that project I plan
to add a water jacket which should improve beam quality by reducing thermal
gradients.

The following things occurred to me, after I considered that picture for a
while:

If you switch with a spark gap, you need at least 10 amps going through it
for some ns to develop a good conductive channel & make the switch close
smoothly & thoroughly.

There is no earthly reason why this device has to be balanced. That is, the
cap on the left can have an entirely different value from the cap on the
right.

What I did was to use an old Maxwell low-inductance cap with stripline
termination as the one on the left, and a pair of barium titanate "doorknob"
caps, each of 3600 pF, in series as the cap on the right. (I had to put them
in series because their voltage rating was not high enough.)

The Maxwell is rated 0.089 uF at 75 kV; I've never taken it over about 35,
partly because I do not care to X-ray myself too heavily. See:
Jon's
Lamp Driver.

How it works: When I trigger the spark gap (an old EG&G device that is
designed to work when there's anything from 25 to 69 kV across it), the cap on
the right promptly discharges through it, causing many amps to flow & closing
the switch rather firmly. I haven't actually been able to measure this, but it
seems likely that this creates a tank circuit that rings down to perhaps minus
half of the initial charging voltage, V. (A proper LC inversion circuit, BTW,
probably rings down to at least -0.8V. I doubt that my thing is anywhere near
that good.)

One way or the other, this doesn't take very long, because the capacitance &
inductance are both very low. My first guess is that it's no more than 50
ns. At the end of this time the switch is shut very firmly, and there's a
HUGE voltage across the flashlamp. Overvolting the lamp fast & heavily is a
good way to accomplish two things: (1) it turns the lamp on much better than a
slow rise in voltage, and (2) as I learned to my regret, it has a much better
chance of blowing the lamp to hell.

The first two lamps I tried in this thing were beautiful things. They had 6"
arc length, and were 5 mm ID, 7 mm OD. They were brand spanking new. I got 'em
surplus, for $15 apiece, after which the place that was selling them raised
the price to $50 and I could no longer afford them. Sigh.

Anyway, at 23 kV (below the actual lowest rated voltage for the switch), it
took just 3 pulses to blow up each of my nice lamps. I then switched to an old
capillary-bore lamp with only 4" of arc length and about a 1 mm or maybe 2 mm
bore. I have several of these and I figured I could blow a few up & still have
a laser. It turns out that this lamp holds things back enough that it is
stable even as high as about 35 kV. (At 1/2 * C * V2, with C in
farads and V in volts, that's right around 40 joules at 30 kV or 54.5 joules
at 35 kV, unless I have my head on backwards tonight.)

With this lamp, and running at 30 kV if I recall correctly, the driver was able
to threshold a dye cell without any mirrors. It's a well-aligned cell, of
course -- the end windows are serving as the mirrors -- but that's not a whole
lot of feedback, and you can demonstrate for yourself that it isn't all that
easy to threshold a naked cell: just try it. I only did it with fluorescein
and with Rhodamine-6G, near as I recall, though I bet I could have done it
with Rhodamine-B in glycerol as well -- Rhodamine-B is a very reasonable dye in
glycerol or plastic, much better than it is in water or isopropanol. (For
whatever reason, it has very high fluorescence quantum efficiency in solvents
with very high viscosity.) Believe I tried with 7-diethylamino- 4-methyl
Coumarin & failed, no real surprise -- that's a harder dye to work with than
fluorescein or R6G, by a fair margin.

(I should mention that I just wrap aluminum foil around the lamp & dye cell -
close-coupling of this sort is a win as far as I'm concerned. MUCH easier than
trying to make one of those fancy ellipsoidal reflector things and probably at
least as effective - not so much room for light to fall out the ends!)

The first top photo shows some R6G, lasing with an orange output. The other
photo shows some 4MU lasing with an intense blue output. I really like the
color in the output from the 4MU.

Many thanks to Jon Singer and Milan Karakas for helping me to do this.

Here are some videos of one of my dye lasers, with the
output passing through some water vapor. It's noisy, because the
entire setup is powered with a mechanical generator and a spark gap
switch. The dye is R6G, which produces a yellow-orange laser output.

Also, here is a comparison between low frequency and high frequency HV
sparks from my Wimshurst Machine. As with electronic circuitry, the
capacitors control the frequency. The size of the capacitors also
determine the current (and thickness) of the HV sparks, as well.

Additional Information on Home-Built Dye Lasers

The article in "Light and its Uses" claims that this flashlamp will fire at
about 60 Torr using the recommended capacitor of 15 uF at 3 kV. This is not
true (not even close). The actual pressure that will cause discharge of this
capacitor is more like 8 to 9 Torr.

P is the actual pressure in Torr; Pd is the pressure at which the discharge occurs.

V is the applied voltage; Vb is the breakdown voltage.

d is the distance between the electrodes of the flashlamp.

For the flashlamp suggested for the dye laser with approximately 82 mm
between electrodes, one can calculate a breakdown pressure of 8.8 Torr, NOT
60 Torr! Thus, either the vacuum system will need to be somewhat better or
the flashlamp dimensions adjusted accordingly.

I don't know whether the approach described below can be made to work without
extraordinary effort (or for other types of laser dyes) but it would certainly
appear that the electronics at least would be a nice challenge! His not
very special energy storage capacitor and not very high voltage must not have
been that mundane to produce 6 J in a 2 us pulse!

(From: fatusa@netscape.net.)

Lasing of Rhodamine-6G can be done with a regular garbage strobe tube (glass of
linear dimensions - without crazing in glass) by attention to several points
including: very tight coupling of strobe/cell, use of confocal cavity with HeNe
laser mirrors, and a fairly strong molar dye solution. But the most important
thing to do is a prepulse technique - to first hit the tube with a pulse of low
energy (say 10 amps) and then hit it harder 5 to 10 us after the prepulse.
Do not expect much output. For mine (done a while ago) with a prepulse of
0.5 J and main input pulse of 6 J, lasing broad band was achieved reliably and
repeatably at a low rep rate in a portable system. The main pulse had a rise
time of approximately 200 ns and was 2 us wide. Better results can be achieved
if a triplet quencher is used as well. The main cap was not a "special" and
the voltages were mild (relatively), but the electronics, etc. are not trivial.

If I use the OC/HR (Output Coupler/High Reflector mirrors) from a HeNe and a
dye that peaks around 630 nm would I get any amplification? I have Kiton-red
and Rhodamine-B both of which should peak around the HeNe red line.

(From: Jon Singer, of the Joss Research Institute.)

If you pump correctly, either of these should
lase; but because HeNe has much lower gain than dyes, the HeNe output
coupler is seriously not the right tool for the job. Dye laser output
couplers often pass as much as 25 or even 50% of the light that hits
them. If you intend to lase Rhodamine B, BTW, use a viscous solvent
if you can; from what I've read it has lousy fluorescence efficiency
in methanol (0.43), but by the time you get to glycerol it is highly
efficient (0.96 or so). The problem with glycerol is getting the
solution out of the dye cell after you pulse it; maybe propylene
glycol is a reasonable compromise, or a mixture of glycerol and
water...

(From: Jacob Conner (jake@westplainsonline.com).)

The OC/HR are from a Hughes HeNe. I believe they are dielectric (look blue
when you look through them) and the optical resonator will be external to the
dye cell which is a quartz glass tube with quartz ground glass windows (not
sure if I should place at the Brewster angle) and there are 2 "T"'s coming
out of the cell for dye circulation

The quartz tube is cemented to two brass T pipe fittings using Epoxy. The
pump lamps are going to be either a pair of 300 W halogens or 2 xenon flash
lamps. I hope this will work. if so i will invest in some other optics so I
can go tuneable since the HeNe mirrors do have a small bandwidth I can
probably insert a prism in the cavity for "some" tuneability

(From: PandaSnax (pandasnax@aol.com).)

It sounds like you are going in the right direction so far. I'd lean more
toward the Xenon flash tubes myself because they tend to put out a lot of UV
and their use is highly documented. Unfortunately unless you build them
yourself they tend to be pretty pricey. However two that flash alternately can
give you a pretty high flash rate and some specialized tubes working together
can give you continuous operation. The next question to ask is how are you
going to flow the dye through the dye cell?

(From: Dan Mills (Dmills@abcde.demon.co.uk).)

Forget the TH lamps! You will not get enough light. I would go for the Xe
flashlamps and would probably use a pair. It is worth getting a copy of the
EG+G Electro optics catalog as this gives lots of detail on the design of
flashlamp circuitry.

Note that even if you could get sufficient optical power from the halogen
lamps your design will probably not lase continuously. I do not think
that a liner flow dye cell is capable of
a high enough flow rate. I attempted to build a dye laser similar to your
design using a continuously burning SBA Xenon lamp in a old projector lamp
house as the pump source. It was not enough! This was running 900W at 2-3
times the efficiency of a TH lamp.

I have considered attempting to use a DC arc welder to power a carbon arc lamp
as a pump. Anyone else attempted this?

(From: Jacob Conner (jake@westplainsonline.com).)

The Scientific American dye laser lamp talked of getting 5 kW output from the
laser. Is this possible with a home made flashlamp? The airport here has
some hefty xenon strobes :) I want brick busting performance here ;)

(From: Dan Mills (Dmills@abcde.demon.co.uk).)

Yea you can get 5kW output pulses. (Not 5 KJ) The pulse duration is really
short and the PRF is fairly low. Average *INPUT* power in the scientific
American design is around 70W, at 1 PPS Average output is probably in the
order of milliwatts.

It is probably not possible to obtain more then a watt average output from a
home made dye laser. I would recommend you consider a liquid cooled pulsed
YAG. This will give your 'brick busting performance' especially if you can get
the local radar tech to get you some of the caps they use in the pulse forming
network for the radar! You can make a suitably cooled yag lase
continuously. Pulsed would probably be better for you.

(From: Dan Mills (Dmills@abcde.demon.co.uk).)

I have considered attempting to use a DC arc welder to power a carbon arc lamp
as a pump. Anyone else attempted this?

(From: Heath Edwards (heathe@citi.w1.com).)

I use my Lincoln AC arc welder with a twin-carbon arc torch. The carbons are
3/8" diameter and copper plated for strength. I wouldn't recommend this type
of torch because the carbons burn down fairly rapid. Just having done some
light brazing with the torch the rods have shortened several inches. Which
means you would need to have an automatic rod adjuster.

Now if you used larger diameter rods, they might run longer. But they'll
require more current.

The light intensity is certainly high! You HAVE to wear welding goggles with
a dark lens of #8 or better.

(From: Mike Poulton (tjpoulton@aol.com).)

I would like to build a dye laser for use in light shows and classroom
demonstrations. I have built several lasers, but never completely from
scratch. My question is about an interesting phenomenon which was referred to
in a small piece of literature about dye lasers. It seemed to imply that if
you direct the beam of a nitrogen laser through a chamber containing a dye
used in dye lasers, it will cause the dye to lase along the path of the
nitrogen laser beam, and where the beam exits the other side of the chamber,
it will have been converted to a visible beam from the dye. No resonant
optics involved. If this works and is true, please tell me, because that
means that I don't have to align any resonant optics! If this does not work,
please inform me of that, too. Any other information on dye lasers would be
appreciated.

(From: PandaSnax (pandasnax@aol.com).)

I read in one of Jeff Hecht's (sorry if misspelled) books that this is a
viable technique but that for most applications the dye is contained in an
optical chamber that is semi-resonant, i.e. one partially reflective
output mirror.

(From: Charles Nelson (cnelso01@merit.edu).)

The reason is similar to why Nitrogens don't really need mirrors, or if any
are used that only as a high reflector and not an output coupler. The gain is
very high with using a nitrogen as a pump so you get a very large population
inversion. Try also using some Day-Glo plastics such as those used in rulers
and the like.

(From: somebody (p.g@worldnet.att.net).)

I have built a variety of flashlamp pumped dye lasers including the one in
Scientific American.

The only way I have gotten them to work is to pump a huge amount of energy in
to a two mm bore dye tube. I had to use two 150 uf, 1000 V capacitors with two
xenon flashlamps with the proper inductors. I also had to experiment with
different dye/solvent mix ratios. the easiest dye to get to lase is
Rhodamine-6G. these type of dye laser are to say the least, a pain in the a**
and not much worth the effort. the best way I have found to make a dye laser,
is to pump it with an UV laser.

I made the nitrogen laser in from Scientific American but scaled it up to one
meter in length. it uses no mirrors and it will operate with ordinary air at
about one torr. all though using pure nitrogen will give much better
performance. I simply focused the beam onto the surface of the dye with a
cylindrical lens and got fantastic results. no mirrors required but using one
mirror at one end will get you twice the output.

(From: Jon Singer, of the Joss Research Institute.)

The reason lamp-pumped dye lasers generally can't be made to lase
continuously is strictly a thermal issue, not a matter of self
terminating population inversion. Dye is NOT self terminating;
the lower laser levels (of which there are lots, not just one)
are essentially thermally excited levels of the ground electronic
state, which depopulate (to a Boltzmann distribution) in about
10-12 seconds. In support of this, I offer the fact
that CW dye lasers not only exist, they have been commercially
available for more than 3 decades.

The reason why a flashlamp-pumped dye laser has to be allowed to
relax between pulses or after a few pulses is that the dye solution
gets hot when you lase it, and develops refractive index
irregularities (these are called "Schlieren"), just like the wiggles
you can see in the shadow of the exhaust from a bus or a truck on a
sunny day, or so-called "heat waves" over an asphalt road in the
summer. These irregularities prevent the light from passing straight
through the dye. You either have to allow the temperature to achieve
a smooth profile in the cell, or you have to move fresh dye solution
into the cell to replace the hot stuff.

(From: Jon Singer, of the Joss Research Institute.)

I'm afraid this is a sad example of a fundamental fact about capacitors:

Energy = 0.5 C * V2

A thousand volts just isn't the way you want to run a lamp driver for
a dye laser. 300 uf at 1,000 V stores 150 joules; at 20 kV it takes
less than 1 uf! The much smaller cap will discharge much faster,
especially if it's a design that has low Effective Series Inductance
(ESL) - 20 nH or less seems to be quite decent.

Notice that you had trouble lasing anything, even with 150 J into
the flashlamp, whereas a driver that ran at high voltage, used a fast
0.1 uf cap, and was constructed with reasonably low inductance had
absolutely no trouble lasing any of several dyes with 25 joules or
less, in a tube with 4 mm bore. In other words, far from being a pain
in the butt, this type of dye laser is actually quite easy to build
and work with, provided that you are willing to run at 20 kV instead
of 1 kV.

I ended up tight-wrapping the lamp and the dye cell with aluminum
foil, the way I always do, because the white reflective material in
the head was nonviable. (I don't use ellipsoidal reflectors for lamp-
pumped dye lasers -- they are much more trouble than they're worth.
Aluminum foil is cheap and easy, and it works just fine. Remember,
shiny side in! Remember, also, that both the flashlamp and the dye
cell have to be made of fused silica, else you are looking for
severely reduced efficiency if you actually get lasing at all.)

The "eBay Head" laser was quite crude, but it worked very well
even so. (I took it out of service so I could work on one of
the nitrogen lasers, which is why I speak of it in the past tense.)

BTW, there is what I hope is an amusing "photographic tuning curve"
for Rhodamine 6G toward the bottom of that page -- I didn't have
the monochromator running at that point, and I figured that if I
could get the camera to show the colors even moderately well, it
would make a cute set of pictures.

The newer "Minimalist" laser stores only 12 Joules in its capacitor
bank, but lases the usual dyes quite handily. So far, it has
succeeded in thresholding Rhodamine 640, Rhodamine 6G, Fluorescein,
Fluorol 555, Coumarin 1 (7-Diethylamino-4-Methyl-Coumarin),
4-Methyl-Umbelliferone, and two handy DIY laser dyes: Dharma
Trading Company's "Optic Whitener" (which is mentioned elsewhere
on this page with a link, and is particularly nice for nitrogen
laser pumping) and an isopropyl alcohol extract from a
Sharpie™ "Accent" yellow-green highlighter marker.

In Its current
incarnation (as of early February, 2010), it uses a single-stage Marx
generator built from a pair of 30-nf Maxwell capacitors that I got on eBay,
charged to 20 kV, running a flashlamp that I bought for $16 from
the Electronic Goldmine.
(Search for "Large High Power Xenon Strobe Tube". It isn't actually
large; the arclength is only about 4".)

This laser is a fine demonstration of what I pointed out above,
about small capacitors at high voltages. I was actually able to
threshold R640 with only 6 J in a single 30 nf Maxwell, before I
shifted to the Marx generator design.

On the issue of mirrors, I suggest that for the total reflector, a person use
a first surface mirror, which can be very easily obtained from an old
photocopier, laser printer or wholesale place like Edmund Scientific. For the
output coupler, on low power dye lasers, a piece of Mirro-Pane, which is used
for two way mirrors will work nicely. Normally, a local glass shop will give
you a sample for nothing. :-) The transmittance is about 30 percent or so,
which works well for the small laser.

Next, the question of pumping a dye laser with 300 watt halogens is a waste of
effort. Organic dye requires a far, far more intense light source than that to
reach threshold. Even the airport runway lamps are not quite right for a dye
laser. Xenon flashlamps have to be specially designed to be driven to
extremely high current levels to pump dye lasers efficiently. Normally, this
is combined with high current simmer to ensure long lamp life. The ablative
wall lamp, as described in the article, is really the best source of light for
the homebuilder! This type of lamp can easily be scale up to any size
desired. Furthermore, it is very inexpensive and simple to construct. The
pumping cavity design is important as is a reasonably fast discharge circuit.

The one, single most important thing that was not used in the Scientific
American laser, is an infrared filter of some sort, between the flashlamp an
the dye cell! For a flash pumped laser, this will make the difference between
a working or non working laser. The reason is this: When the flashlamp fires,
it produces a very intense pulse of light throughout the ultraviolet, visible
and infrared spectrum. The dye solution, whether alcohol or water based, has
very strong absorption lines in the mid infrared. If the dye is allowed to
absorb this radiation, a VERY strong shock wave appears at the edge of the dye
cell wall and travels in toward the center of the dye solution. This shock
wave completely destroys the optical homogeneity of the dye solution and
terminates the laser pulse almost as fast as it can begin! (less than one
microsecond) Lankard was not aware of this effect, as it had not been detected
at the time that the article was written. For the folks out there who have
gotten this laser to work, I would bet that you got a very divergent laser
beam. As opposed to the tight beam of say a HeNe, right? This was caused by
the infrared shock wave! If a filter is used, the laser will produce a much
nicer beam and will lase for quite a bit longer. This translates into more
energy out. For an infrared filter, I suggest that a second tube be placed
around the flashlamp and water flowed though the annular space between the two
tubes. That way, the water jacket absorbs this infrared radiation before it
can get to the dye cell and ruin the performance of your laser. Of course, the
water jacket must not be extended to the electrodes of the flashlamp or the
water will short the lamp out. (unless deionized water is used)

There is a very good paper that was published in Applied Optics Vol 13, No.
2, 1974, by Fisher and Ganiel in which they describe the shock wave problem
and even photograph the shock waves.

Finally, the amount of pump energy in the Lankard laser is somewhat low for
the design. If a person were to scale the laser dye cell to say 6 mm bore with
a length of 5 or six inches, they would be better off. For the matching lamp
to go with that, I would suggest a lamp of 6 mm bore and arc length equal to
the dye cell length pumped by capacitor of maybe 5 microfarads at 10 kv. (Low
inductance and high current discharge capability should be specified to the cap
manufacturer) This would give an energy storage capacity of 250 joules which
should be plenty to reach laser threshold. Also, dropping the lamp pressure
to just a couple of torr and firing the lamp by use of a simple spark gap will
make the rise time of the lamp faster and really help in the efficiency of the
laser.

This only touches on the improvements that are possible with the dye laser. :-)

As to potential output of the dye laser. For the Scientific American laser, 5
kW would be "maybe". ;-) As to the output that can be had from a homemade dye
laser, the last one that I built produced 5 joules in a 3 microsecond pulse
with a peak beam intensity of well over a megawatt. The beam diameter was 1 cm
and divergence was about 1 mr, a nice clean beam. The one that I am building
now should easily do 9 joules in about 2 to 3 microseconds.

One thing that should be touched on again, is that it only takes less than 25
MICRO joules of energy at the Rhodamine-6G wavelength of 590 nm. to do
permanent damage to the eye. These lasers must be used with great care to
prevent serious injury!

Also, the energy discharge circuit for the flashlamp is potentially LETHAL if
you are careless! All it take is once!

As you will discover, there is no absolute 'best' dye concentration
to be used in these types of lasers. There are certain parameters to
which one may adhere in order to produce desired results regarding the
peak wavelength emission within the tuning curve of each dye. Different
dye concentrations as well as the choice of solvent will affect the
output wavelength to some extent, with higher concentrations shifting
the output toward the longer wavelengths. In general, laser-pumped
dye cavities usually contain higher dye concentrations than are commonly
employed in flashlamp-pumped dye cells.

A concentration like 0.8 g/l Coumarin 460 in pure ethanol is common for N2
laser-pumped dye lasers and should perform as expected if all other conditions
are met including sufficient pump power and proper focusing of the pump beam.
The Coumarin derivatives will likely 'lase' superradiantly (without need for a
resonant cavity) if the pump flux density is adequate.

Common concentrations of Rhodamine 6G in ethanol for a N2 laser pumped dye
laser application are usually in the 1 to 2 g/l range. This appears as a
yellow/orange fluorescent liquid.

In order for a dye laser to be pumped successfully, the light source must
produce an extremely high peak intensity in a short period of time. This
greatly limits your options. About the only approach that might have any
chance of working is something like a mercury discharge lamp or solar furnace.
See the section: Mercury Vapor Lamps to Pump
Dye Laser? but your probability of success isn't very high.

And the answer to your next question is: No, you can't pump a conventional dye
laser with the laserdiode out of your CD player or likely even a high power
laser diode for that matter. :-) However, a different sort of design might
work. See the section: Diode Laser to Pump
Dye Laser.

A typical question goes like:

"Say I took a 100 W light bulb and surrounded it by a sphere that was coated
inside with a 100% reflective mirror and made a little hole in a place on one
side of the sphere. Then, in time all the light would come out of that hole.
Would the power of the beam be 100 W or would there be no beam because
it's a multiple wave length light?

Just wondering"

The short answer is: Forget it. Despite how bright a large incandescent (even
a halogen) bulb appears, it converts only a few percent of electrical power to
light output. And, even less of it is going to be at the absorption band of
the laser dye.

(From: Terry Greene (xray@cstel.net).)

What you will get is one very hot globe.

No reflector is 100 % efficient. After dozens of bounces most of
the optical energy coming from the bulb will become heat.

Power ratings on light bulbs is a measurement of INPUT power. Incandescent
light bulbs are very inefficient converting only a few percent (can't recall
average number, anyone?) of input power into optical energy. A 100 watt
light bulb will only have several watts of optical output.

(From Steve Roberts.)

There has only ever been one non-laser pumped or non-flashlamp pumped dye laser
experiment that I have seen documented and that used 7 huge custom made CW
xenon arcs to pump a IR dye. The input power was far greater then required for
even a small ion laser. The lamps were driven beyond their specified maximum
power and lasted about a hour.

The particular dye was chosen because it is one of the few that wouldn't fall
pray to triplet state quenching. It did 15 mW in the IR at 1100 nm or so. No
currently known dye that can lase in the visible can hold up to continuous
lasing because it will be overpumped into the next nonlasing level in something
far less then a microsecond. This is why CW dye lasers all have flowing jets
and even rapidly pulsed dye lasers of any significant power have fast flows.
You have to get the old still somewhat excited dye out of the lasing path as it
then has a high adsorption and will literally turn itself off. Those well
funded researchers were looking for a easier way to get laser emission - for
years - and that was the best they could come up with.

You're not going to get anywhere near the pump threshold with a sun pumped dye,
yet a simple home made nitrogen laser will do it, the wonders of quantum
mechanics. :-)

(From: Jon Singer, of the Joss Research Institute.)

I had no idea that anyone had ever successfully pumped a CW dye laser of any
sort with lamps, and was astounded to see mention of it. Wow! No surprise
they had to exceed the ratings on the lamps.

Hmmm  it turns out that there has been at least one other
instance. It used Rhodamine 6G, and it was published in 1988 (!). Here
is the reference:

Abstract: Continuous-wave operation of a Rhodamine 6G dye laser,
incoherently pumped by a high-pressure argon arc, has been achieved. A
special electrode design reduces melting of the electrode tips, and thus
the arc provides the necessary brightness for periods of the order of
hours.

(I believe they had to push 8.8 kW through the arc lamp, so this is not
exactly a DIY project.)

A Townes-Schawlow calculation will tell you that for a reasonable solution of
R6G, you need about 5 kW per cubic cm of dye to bring the thing to threshold
if your active region is maybe 10 cm long.

If memory serves, the Townes-Schawlow criterion (which gives you the number
of excited centers per cubic cm that you need in order to reach threshold)
is pretty simple:

N0 = 8π n2 (1-R1R2) τ Δν / λ2 L φ

Where:

N0 is the threshold number of excited centers
per cubic centimeter

8π is a geometrical compensation factor

n is the refractive index of the laser medium

R1 and R2 are the reflectivities of the mirrors.

τ is the fluorescence lifetime, in seconds

Δν is the emission bandwidth, in Hz (you’ll
have to figure it out in nm and convert; remember, this is
not the laser bandwidth, but rather the bandwidth of the
fluorescence peak)

λ is the center wavelength of the emission band, in cm (not nm!)

L is the active length of the cavity, in cm

φ is the quantum efficiency of the fluorescence.

Remember, this calculation ignores all loss sources
other than the output of the laser, so it is wildly
optimistic. At the very least, you should double or
quadruple the number it gives you.

Δν is more difficult; I’m going to use 2200
cm-1, which is perhaps a bit narrower than the
actual fluorescence peak, but is wider than the usual
tuning range. In Hz, this is very close to 6.6x1013,
so that is the value I will use.

λ is 5.9x10-5 (remember, it’s in cm), so
λ2 = 3.48x10-9

L is 10 cm

φ = 0.96 or so -- Rhodamine 590 is a very good dye.

The numerator evaluates to something so close to 7.35
that I'm just going to stay with that.
The denominator evaluates to 3.34x10-8.
Putting them together gives us 2.2x1013; that’s
2.2x1016 per liter, which is approximately
3.6x10-8 molar,
actually only about a factor of 5 low. Not bad, all
things considered. Remember, for any real system, you
need to use more dye and push harder.

Now: how much power do we need to apply?

Let’s assume that the dye cell holds 1 cubic cm of
solution, just for convenience. That takes 2.2x1013 photons.

2.2x1013 photons, however, is only part of the story. We
can’t dump them all in at once, and the dye is
fluorescing while we try to pump it, so I am arbitrarily
going to say that we take one fluorescence lifetime,
give or take a little, and we use twice the calculated
number of photons to compensate for the fluorescence loss.
That is, 4.4x1013 photons over 5 ns.

I'm also going to say that the average energy of a
pumping photon is 3.5 eV, which (if I am not miscalculating)
corresponds to a wavelength of just over 350 nm. This is
probably fairly reasonable.

1 eV = 1.602x10-19 joule, so 3.5 eV times 4.4x1013
photons is about 25 microjoule. If we apply that in 5 nsec, the
resulting average power is just under 5 kW. Q. E. D., kids:
the absolute minimum you could ever hope to run a Rhodamine
590 dye laser with, in a 10 cm dye cell with a 95% reflective
output coupler, is 5 kW... but there's something you
have to remember: that 5 kW is the actual amount of power
absorbed by the dye. Anything the dye fails to pick up
doesn't count. In order to put 5 kW into 1 cc of R590
at usable wavelengths you have to put well over a megawatt
of electrical power into a flashlamp, and that ignores all
of the other possible losses that can drive up the threshold.

I hope you now see why only two or three groups have ever produced
a fully CW lamp-pumped dye laser. Very few CW lamps are capable of
this level of service; that 5 kW is the actual power absorbed by
the dye solution, so the input power to the lamp is ridiculous.
It is also difficult to move the dye fast enough to keep it from
developing significant optical inhomogeneities, which ruin the
optical path and cause lasing to cease. (The first laser-pumped
CW dye laser needed to have its dye solution move through the
dye cell at 2 meters per second, and that was just to get the dye
past a "hot spot" a few microns across.)

I do like the idea of doing it with laser diodes; they are getting cheaper and
cheaper, even with reasonable output power. A DiY diode-laser-pumped CW dye
laser would be quite something.

"Does anyone here know if any of the organic dyes can be optically pumped to
lasing with a mercury vapor light of sufficient power? If so, what is the
minimum wattage needed?"

(From: Don Klipstein (don@donklipstein.com).)

Organic dye lasers tend to require much higher degree of pumping than a
mercury arc can provide. This is due to the short lifetime of the desired
excited state of organic dye molecules (typically around a nanosecond or a few
nanoseconds). You have to have a light intense enough to achieve the
necessary population inversion in about this amount of time.

(Since these lasers are usually 4-level lasers, you don't actually have to
excite a majority of all dye molecules within a nanosecond. However, what you
have to do is still a tall order.)

In fact, plain ordinary xenon flash tubes often have difficulty achieving the
necessary light intensity. You may need extra-intense flash tubes with
somewhat unusual circuitry, voltages, etc. to get a dye laser working.

For some xenon flash tube stuff including stuff that may help getting a dye
laser to lase, try these web pages of mine:

As of several years ago, the dye I have heard of as most suitable for a
do-it-yourself dye laser is Rhodamine-6G. The more available Rhodamine-B and
Uranine (or Fluorescein in alkaline solution) can work, but generally not as
well. Adding glycerin or the like to make the solution more viscous is said
to have a beneficial effect, but probably makes little difference in the
extreme pumping requirements of aqueous (or alcohol) dye solution lasers.

For a similar type of laser construction that has a much lower pumping
requirement, use an appropriate compound or chelate of europium. I have heard
of this being capable of king a "dye" type laser that can be pumped from the
intense light of a solar furnace, and this may work from an intense enough
mercury arc.

(From: Thomas A Suit (tsuit@osf1.gmu.edu).)

Solar furnace?? Yeow!! The dye laser I saw in operation up at LLE was pumped
via YAG light frequency doubled to green. I put my hand in the green beam and
it felt like a candle flame. I rapidly pulled my hand out. :-) The KTP
frequency doubler was said to be 20% efficient. No way was my hand going into
the IR beam. A solar furnace would be much hotter than a candle flame.

(From: Don Klipstein (don@donklipstein.com).)

The working europium compounds emit a highly visible orange-ish red wavelength
in the low 600's of nm wavelength. Any europium based stuff that will work
will have at least some visible reddish, orange-reddish or pinkish
fluorescence in ordinary daylight or most high-pressure mercury light.

Please note that most fluorescent inorganic and inorganic-based substances
fluoresce only or mainly from shorter UV wavelengths that damage many organic
substances (including chelates?). It may be a bit tricky getting an europium
based substance that can be pumped from wavelengths that don't harm it.

What I have seen (several years ago) seems to discourage europium based liquid
lasing medium lasers as having the disadvantages of both inorganic and dye
lasers.

(I suspect conspiracy mode)

I wonder if this is to discourage the obvious hazards of telling anyone how to
make a Class IV laser that hobbyists can make in their basements. (Minor
remote accidental fire-starting hazards, moderate skin burn hazards, and
extreme hazards of accidentally causing permanent eye damage in
milliseconds.)()

Anyone who knows how to get this to work, or names/sources of appropriate dyes
or euoropium compounds, please post and/or email to don@donklipstein.com.

(From: Joshua B. Halpern (jbh@ILP.Physik.Uni-Essen.DE).)

Lamps are not, in general, intense enough unless you pulse them with a
powerful fast current (flashlamp pumped dye lasers) Mercury lamps are a bad
choice because the UV (253.6 nm??) light tears the dye molecules apart. If
you are looking for a pump laser that you can build yourself (you assume all
risk, etc.) There are several designs for simple nitrogen lasers (337 nm)
that can be found in the journal: Review of Scientific Instruments (late 1970s
and early 1980s) and one design was published in the Amateur Scientist section
of Scientific American.

These can easily pump a small dye laser.

(From: Michael Solonenko (misha@vm.temple.edu).)

You need high pump power densities to get anything out of the dye. At the same
time, the dye gets easily destroyed if continuously irradiated with powers
much less than the one necessary for lasing. Hence, the dye flow, cooling and
filtering should be set up. In the industrial lasers (Coherent), ~6 W of an
argon ion laser (~448 and/or 514 nm) is focused, as noted before, in ~30
micrometer spot on a dye jet to get the job done. See if the total power of
your lamp in the absorption region of the dye you are going to use can provide
comparable power densities (take 6 W/30 um as a total power density for a
laser).

You just might get lucky if you:

Have enough power density from the pump lamp;

Cool, filter and have the dye flow fast enough to prevent photochemistry;

Use confocal resonator with good dielectric mirrors.

But, I'd warn you, the wavelength of such a laser will be extremely unstable,
shifting randomly in the region of 10 to 20 nm around the dye's emission
maximum with the increments of intermodal spacing.

(From: Jens Decker (dej05093@rchsg6.chemie.uni-regensburg.de).)

I don't think it is possible to get a CW laser running with any lamp. Even a
standing wave laser need's about a Watt focused into a very small (about 30
microns) spot of a thin dye jet. You can't focus the light of your street lamp
(a really nice tool for photochemistry!) to such a small spot. Dielectric
mirrors are essential too.

Maybe it would be possible to pump a standing wave dye with a telescope using
a single mode fiber to couple the moving telescope with the laser?

Building a small N2-laser or using flashlamps for pumping a self made pulsed
dye laser should be possible. In two resent papers in the journal: Review of
Scientific Instruments, bright blue LEDs have been used as pulsed UV sources
which might be useful as a pumping source.

(From: Joshua Halpern (jbh@IDT.NET).)

The strongest lines from the mercury vapor lamp are in the UV (the
intercombination 253 nm line, and if you contact the lamp directly to the dye
cuvette, the resonance 186 nm line. By the way it is the latter which
photodissociates oxygen leading to the formation of ozone that you should be
smelling if you operate this lamp in the air). These emissions have a high
enough energy to break R6G apart. That is a bad idea if you want to build a
dye laser. The peak of the R6G absorption is in the green. You would be
better off with a strong green or white light, with a UV filter on it.

You would also have to have a huge CW lamp. AFAIK, it has not been done, but
rather one uses Ar-ion lasers, or pulsed lasers or flashlamps to pump dye
lasers. There is a report of a sun pumped dye laser (Israeli?) in the last
few years, but how big the collector is I do not know.

(From: Dave (skeeve@excellentproducts.com).)

I believe that you will not be able to reach lasing threshold of R6G with a
mercury vapor lamp unless you do some fancy trickery.

The output of a 1000 watt mercury vapor lamp is at lease 25 times too low to
lase organic dye, however, one research team found that if they set up a
mercury vapor lamp with a special power supply which could run the lamp at
about half power continuously and then discharge an energy storage capacitor
through it, they could reach the intensity level that was needed to pump a dye
laser. The pulsed light of the lamp was about 100 times brighter than the cw
emission of the lamp. Of course this laser operated in a pulsed manner. What
was really interesting, though is that the mercury vapor lamp which was
operated in this way, altered from the normal emission spectrum of the mercury
vapor lamp so that the emission spectrum matched really well to the absorption
curve of R6G and other dyes.

Indeed, it was compared to a xenon flashlamp at the same discharge energy and
the comparison indicated that the pulsed mercury lamp should be a much better
pump source for visible spectrum organic dyes - especially those in the blue.

Abstract: A high pressure Hg capillary amp (PEK AH 6-2-B) has been
successfully pulsed to produce laser action in a methanol solution of R6G.
This lamp may provide a better laser efficiency than that available with a
xenon flashtube.

Abstract: Calibrated spectral measurements of the light emitted by a pulsed
high-pressure mercury capillary lamp are presented. These pulsed lamps have
been used in a previous work to pump a Rhodamine-6G laser. The measurements
presented here show a very high efficiency in the blue and near UV part of
the spectrum, suggesting that these lamps represent a very attractive pumping
source for dye lasers emitting in the blue. In particular, as an example, a
computation has been made for a basic solution of 4-MU yielding a spectral
efficiency of 24%.

If you are determined to try a mercury vapor lamp, be sure to check out these
papers, as they have lots of good info in them!

No, you can't just replace the flashlamp in your home-built dye laser with a
bunch of salvaged laser diodes out of old CD player or laser pointers!
(From: A.E. Siegman (siegman@ee.stanford.edu).)
Anyone wanting to play with home-made dye lasers might look at an article by
Richard Scheps, "Low threshold visible dye laser pumped by visible laser
diodes", IEEE Photonics Technology Letters, vol 5, 1156 (October 1993).
Experiments were done using two 10 mW visible diode lasers (a.k.a. "super
laser pointers") as pumps; the threshold was 5.6 mW. The dye was actually in
a 100 micron thick jet, which is not all that easy to make; but I'd bet that
with some care it could be done with a thin dye cell. Also, laser wavelength
was 758 nm, which is not really visible. But also, this was 6 years ago - with
some ingenuity an experimentalist might be able to something similar "at home".
(From: Joshua Halpern (jbh@IDT.NET).)
You can do it using razor blades, or smooth glass plates to form the jet. It
takes a bunch of fussing, and can be pretty messy learning how to do it, but
it works. OTOH, just use the EtGlycol without the dye until the jet is
working. Thin cells will probably have too much reflective loss to work. You
might look in RSI between bout 1974 and 1980 for jet designs.
An interesting idea.

For optimal pumping efficiency, consider placing the flashlamp *inside* a
coaxial dye chamber (this could also be applied to other types of optically
pumped lasers). Surround the entire affair with a cylindrical reflector.
In this way, one would think that virtually 100 percent of the optical energy
from the flashlamp will be absorbed by the lasing medium as it bounces around
inside the cylindrical reflector. However, at high current densities, the
plasma in the flashlamp will not be transparent so you might only really get
two passes - out and back.

The laser output will be ring shaped rather than Gaussian and there could be
some unusual mode structure depending you your resonator optics, but for
maximum power and efficiency, this should be unbeatable.

(From: Dave (skeeve@excellentproducts.com).)

Yes, to find a very efficient pumping scheme was the motivation for this
unique pumping idea. If the lamp were in the center of the lasing medium,
(organic dye solution in the case of the article that I refer too), and the
pump light could be completely absorbed in two passes through the dye , from
the lamp out to the reflector and back, then it should be possible to realize
extremely high pumping efficiency. Of course, the output of the laser would be
a ring, and there is the problem of getting the electricity to the lamp, in
the center of the dye cell, but perhaps these obstacles might be overcome. At
any rate, I did not see any further work done in this area, and as I recall,
the author did not build a working model.

I have constructed several standard coaxial flashlamps , but they suffer from
the problem of having half of the output wasted, because it is emitted to the
outer wall of the lamp. In pumping a solid state laser, this might not be a
problem, as the lamp could be driven at a low enough current level that it is
a grey body and the reflector would send at least some of the light back
through the plasma to the lasing medium. In pumping a dye laser though, the
lamp is driven at a high current level which is needed to reach lasing
threshold, (80,000 to 160,000 amps per sq. cm) and the lamp is a true black
body radiator. The reflector that you see around a coaxial lamp is just for a
current return. It does lengthen the pump pulse marginally, but at peak
output, when the plasma is "black", it contributes nothing to the pump light
that gets to the dye cell.

In a later test, Baltakov and the gang went one better and achieved 400 joules
per pulse from a coaxial dye laser. Now that is one mean dye laser! :-)

Dyes are 4-level lasers, so having a dye cell that is much longer
than the active length of the flashlamp shouldn't be much of an issue.
This is true of all regular dyes. (There may be some truly
squirrely weird stuff that behaves differently,
but there's some question as to whether such a
thing could properly be described as a dye laser.) This is a
fundamental property that has to do with the quantum mechanics
involved in dye fluorescence. I can probably find a diagram -
there are several on the Web, but one I just ran into is
in German and is in a discussion of scintillators,
not dye lasers, so it's a bit difficult to follow. ;o)

That said, however, there is always (at reasonable temperatures,
anyway) some thermal population in the lower laser level (which is
actually the rovibronic manifold above the ground singlet electronic
state, but let's not get too involved), and you can excite molecules
out of that population into the first excited singlet, so there
actually *is* a bit of absorption.

This effect is fairly small; but if you take a dye laser running, as
an example, Rhodamine B, and put a cuvette of Rhodamine 6G into the
cavity, you'll probably find that the R6G flashes yellow when you
pulse the laser and orange light from the RB goes through it. (This
also happens if you use the same dye that you're lasing, but because
the color is about the same as the laser's output, it's harder to see
the effect.)

This shows that unexcited dye almost certainly causes the threshold to
be *slightly* higher; but again, the effect is pretty small, and I
wouldn't be too worried about it.

(I showed this effect to a bunch of people in 1971, BTW, using the red
light from a HeNe to pump Rhodamine B (which emits in the orange)
dissolved in glycerol, and told them it was a quantum-mechanical
refrigerator. Cute joke; I didn't think about doing it with a
high-powered pump because there weren't any at the time, and I failed
to think about future developments. Sigh. This refrigerator was
patented within the last few years - needless to say, *not* by me.
Argh!)

The absorption spectrum of a dye almost always overlaps the
emission spectrum. This is one way you can tune an organic dye laser:
if you increase the dye concentration, you push the output toward
longer wavelengths. Unexcited dye in the cavity will have the same
effect. This effect is generally larger than the "B" effect.

If you want to see it, take a dye laser with any handy dye, and run
the output through a monochromator so you know what the wavelength
is. Now put a cuvette of the same dye into the cavity. As you increase
the concentration of the dye in the cuvette (or use a longer & longer
cuvette), so that there are more dye molecules in the path, the effect
on the wavelength should also increase. If you increase the
concentration too much, you may find that the extra dye begins to
interfere with lasing; but that's probably a different effect.

Capacitor size and speed, and relation to dye lasing threshold

Dye laser threshold, for pump pulses that have duration a lot
longer than the fluorescence lifetime, is perhaps best addressed as a
power issue (rather than an energy issue). Basically, because a lamp
pulse is always more than an order of magnitude longer than the
fluorescence lifetime of any dye, you can pretend that you're dealing
with a CW laser. (The lifetime of R6G is about 4.1 ns, and that's
not terribly unusual.)

Assuming that there are no particular problems with things like
Triplet-Triplet Absorption, a given volume of dye solution at a
specified active length, with specified mirrors, requires a certain
level of absorbed power to reach threshold.

You can make a rough calculation of this (see the discussion of
the Townes-Schawlow criterion in the section:
Incandescent Lamps or Other Light
Sources to Pump Dye Laser?.
For R6G in a cell that has 10 cm pumped length, with a
"perfect" max-ref rear reflector and a highly reflective OC (optimized
for low threshold rather than output), you find that the dye has to
absorb 10 to 20 kW per cubic centimeter during the pulse, in order to
reach threshold.

Note that I said that R6G takes 10 to 20 kW per cc, which is higher than
what I arrived at earlier. There's a reason for that: When I redid the
calculation few months ago, I used the actual bandwidth as shown on an
excellent Web site:
PhotochemCAD
Spectra by Category. So the power I got is higher because I
underestimated the bandwidth a few years ago.

If you translate this back to actual electrical power in the lamp it
comes to about 50 MWE, give or take. Depends on how efficient the lamp
is, how much of its output is at wavelengths that the dye can absorb,
and how well the light is coupled from the lamp into the dye
cell. (Also on how much dirt there is in the dye solution and on the
windows and mirrors, but let's not even go there.)

The bottom line can be stated about as follows:

If you can put greater than 5 J into a good xenon lamp with 5" or 6"
arclength in less than 100 nsec, if you can get a good chunk of the resulting
light into the dye cell, if the dye solution actually absorbs a goodly
amount of that light, and if it's a nice friendly efficient dye (like
R6G or Fluorescein), you probably have a chance. ...But if the pulse
isn't fast enough, or if *anything* else is less than optimal, your
chance fades away like the dew on the grass. Thus the Lankard laser
from SciAm, which uses a slow capacitor, an air flashlamp, and a big
lossy reflector, usually takes greater than 100 J per pulse.

(I've said this before, but maybe it's worth repeating: I have a lamp
with 38 cm arclength; my capacitor is 0.1 uF and fairly fast; I'm
charging it to 18 to 24 kV, and switching it with a reasonably fast
triggered spark gap. The pulse is a few hundred ns long. As a result
I can threshold R6G with about 20 J into the lamp, possibly even less.)

It has been pointed out that large capacitors are inherently slow;
but small capacitors are not necessarily all that much faster. You
have to design and build them correctly, and you need interconnections
with very low inductance. (This argues in favor of the
TEA-nitrogen-laser style of construction, which *is* fast. OTOH, it's
not necessarily easy to make a transversely-pumped flashlamp, and it's
not necessarily easy to make a structure of this sort that couples
nicely into a regular linear lamp.)

There may also be some afterglow from the lamp, light that doesn't get
released quickly; this effectively spreads out the pulse. (I recently
saw something suggesting that an air-spark quenches faster than a
xenon lamp. Speaking of which, see the next item.)

Spark versus lamp pumping of dye laser?

Then there is the question of pumping with an air-spark, which has
been raised by several people. That can certainly work. The lowest
threshold I think I've ever heard of was something on the order of 5
mJ into the "lamp", which suggests that if you want to use something
like the circuit that drives a TEA nitrogen laser, a structure that
stores relatively small amounts of energy, a spark may be a good bet.

The trick, I guess, is twofold: 1) keeping the spark confined to a
straight line, and 2) getting as much of the light as possible from
the spark into the dye.

Mercury lamp pumping of dye laser?

I think this has been done. They only got "quasi-CW" operation,
IIRC, and they had to pour a lot of juice into the lamps. (See
the two dal Pozzo articles that are cited elsewhere on this page.)

One thing: I'd expect considerable afterglow at some wavelengths, and
I'm not 100% sure which ones are most likely to display the
effect. Perhaps we get to find out.

Efficiency of dye lasers

Someone said, "I am beginning to understand 'why' dye lasers are less
efficient than common solid state lasers like ruby."

Actually, ruby is awful. Besides, it's a 3-level laser, and it isn't
really comparable to dyes.

Nd+++, in glass, YAG, or YVO4 (or whatever host you happen to like) is
a better example of a solid-state laser with reasonable efficiency (if
it's done well; anything can be built and/or operated poorly).

In any case, if you are pumping a dye laser with another laser, and
you have things optimized and adjusted carefully, it can be quite
efficient -- I think I've seen listed conversion efficiencies on the
order of 35 or more percent. (Even a good lamp-pumped dye laser isn't
*too* bad, though it clearly isn't likely to reach the 35% level.)

Abstract:. The energy and shape of the output pulses from flashlamp-pumped
solutions of rhodamine 6G in isopropyl alcohol were investigated
experimentally as a function of the serial number of a pulse. The
output energy obtained on excitation via a glass filter first increased
from one pulse to another and then began to fall. When the pump energy
was 10 kJ per pulse, the output energy increased by a factor of 1.52 by
the eighth pulse, whereas in the case of ethyl alcohol solutions the
output energy fell monotonically to zero in four pulses. The stability
of rhodamine 6G solutions in isopropyl alcohol exposed to light was an
order of magnitude higher than in ethyl alcohol.

I decided to make RGB "white" light from a single cuvette of dye, pumped
by a nitrogen laser. This is kind of pointless, because you can't get much
power out of it, but I had an interesting time doing it.
See: RGB "White" Dye
Laser Light from a Single Cuvette.

Dye Laser Tid-Bits

Whether you can take any currently available flavor of off-the-shelf Jello(tm)
brand dessert mix and build a working laser using it as the lasing medium is
unknown. However, clear gelatin can certainly be doped with a variety of dyes
to create some sort of a dye laser. But, it might not be tasty to eat. :-)

The seminal paper on this work (I'm serious!) is:
"Laser Action of Dyes in Gelatin", T. W. Hansch, M. Pernier, A. L. Schawlow,
IEEE Journal of Quantum Electronics, January 1971, pp. 45-6. (Thanks to:
Jon Singer, of the Joss Research Institute, for tracking down the reference.)
The authors tried various types of materials for the lasing medium using a
nitrogen laser pump source including:

For a watered down version :) which covers the lasing of Scotch whiskey
fumes and dyed gelatin, see: Schawlow, A. L., "Lasers: The Practical and the
Possible", The Stanford Magazine, Stanford Alumni Association, Stanford, CA,
pp. 24-29, Spring/Summer 1979.

Various other dyes soluble in glycerine mixed with the Knox gelatin in
place of some of the water.

Two commercial gelatin filters, Wratten types 22 and 29.

A normal dye laser was also used successfully as the pump source with some of
these concoctions.

One interesting characteristic of the gelatin medium was that if the incident
pump laser remained stationary, lasing action faded after 100 or so shots.
Some movement was needed, even if quite small, to maintain the response.
Jiggling the Jello was sufficient. :)

The paper is a worth-read. :)

(From: Leonard Migliore (lm@laserk.com).)

According to A. E. Siegman in his book, "Lasers", A. L. Schawlow (who got a
Nobel Prize for his more mainstream laser work) put fluorescein dye in
Knox gelatin and pumped it with a nitrogen laser. After observing laser
emission from this medium, he ate it. It is my understanding that Dr.
Schawlow is alive today despite this activity. (That was in 1998; he died of
unrelated causes in 1999. --- Sam.)

(From: Chris Chagaris (pyro@grolen.com).)

Disodium Fluorescein is one of the few laser dyes that could be ingested
without any ill effects. This chemical is routinely injected into the
bloodstream of patients who undergo fluorescein angiography.

(From: Dave (dyelaser@my-dejanews.com).)

Kiton-Red-S a.k.a. Sulforhodamine-B a.k.a. Acid-Red-52 is another dye that
might be used as well. It is not a legal food coloring in the USA, but it is
used for coloring food in other parts of the world. It is also one of the more
efficient laser dyes. Some of the laser dyes are extremely toxic, but many
others are just slightly toxic or not at all.

(From: Steve Quest (Squest@galileo.cris.com).)

This I did not know. I think it was Red 12 or similar, I know it
wasn't Red 52 that was banned in foods and cosmetics. Is this dye
transparent, translucent, or opaque? The banned dye was opaque.

(From: Steve Roberts.)

Yeah, Jello will lase. I saw the original paper about it at one time. They
used a orange Jello - the dye in it was later pulled by the FDA as a toxin.

(From: Steve Quest (Squest@galileo.cris.com).)

Ahh, I don't buy that. I recall lipstick had a dangerous red dye,
so did red M&M's, but I don't recall Jello having the same problem. The
dye in question was a coal-tar dye, opaque, and not fluorescent.

(From: Steve Roberts.)

The walls of the glass cell were the cavity and it was superradient
when pumped by N2. Otherwise attempts to lase it were with it seeded with
Rhodamine-6G.

(From: Steve Quest (Squest@galileo.cris.com).)

Any transparent thick substance when doped with neodymium,
chromium, etc., will lase. The first Nd lasers (as in Nd:YAG) were
actually Nd:Glass, plain SiO2 glass doped with neodymium. Thus you could
Nd dope clear Jello and I'd bet it would lase when pumped by ruby laser.

(From: Steve Roberts.)

Certain types of DayGlo(tm) plastics will lase with a nitrogen
laser pump as well. I personally can attest that Bud Light(tm) nailed hard with
a excimer lases in the yellow in a dye cavity.

(From: Steve Quest (Squest@galileo.cris.com).)

So will Prestone anti-freeze, when pumped with an excimer. :)
The stuff in Prestone antifreeze that makes it fluoresce is (TaDa!)
Fluorescein. :) Take the stuff under a blacklight sometime. :)
Ethylene Glycol (the active agent) is water clear, the fluorescein is
added so you can see the stuff (glowing greenish yellow).

Fluorescein isn't toxic, but I bet unflavored Jello doped with fluorescein
would not taste good!

You could also dope clear Jello with Nd and pump with ruby. It would lase in
the IR. Given the amount of of Nd required, you could probably eat *it* as
well, without much harm.

(From: Sam.)

So add some suger to the unflavored gelatin. It might even improve lasing!
Then add KTP to the Nd doped Jello laser and get some green light. :)

(From: Matt Polak (skandranon@avians.net).)

In my readings, if I remember correctly, the experiments done with Jello
typically incorporated 'non-toxic' fluorescein dye suspended into the
gelatin in order to actually make it 'lase' when pumped.

I have also heard about beer lasing from multiple sources, usually when
pumped with a nitrogen laser I believe. (vodka also reportedly lases in the
violet region). I've been joking at work (SeaWorld of Ohio - we're owned by
Anheuser Busch beer company) that we should get some money from Corporate
to develop a beer laser for our shows, and run it off kegs of the
corporate product. Of course, there'd have to be extremely strict
quality-control on the lasing medium, which would come in the form of a
spigot in-line with the keg's output flow-lines to allow constant
sampling... err.... testing. :)

Hey L. M. Roberts, how about for this year's LaserF/X technical workshops
we try to get sponsoring for doing demonstrations of which items in the
patented 'Canadian Optics Cleaning Kit(tm)' (i.e., liquor cabinet) will
lase, and their multiple uses for entertainment purposes?

(From: Wes Delaney blkstr@zwallet.com).)

My plan would be to try different kinds, of soft drinks, fruit drinks, and so
on. Although probably not all will work, some might, and some might work
better than others. It is worth pouring a few things from the refrigerator
through the laser cavity. My guess is that some of the fluorescent dyed
Gatorade and Power Ade drinks would probably lase. When I get a dye laser
up and running I intend to do this. You can try anything but, drinks are
fluid so it is easier to pass them through the cavity, and they widely
available.

(From: Harvey Rutt (H.rutt@ecs.soton.ac.uk).)

It is suggested above that neodymium would lase in Jello too.

This will not work. Nd3+ does not fluoresce in hydrogen containing
solvents such as water or Jello. The high vibrational frequency of
the O-H or C-H bond causes the upper state to relax non radiatively.
Liquid lasers were made using Nd3+ but the solvent has to be
hydrogen-free, e.g., POCl3.

Oh, the Jello laser is not a legend. For fun I did it myself back in the
late 60s or early 70s, pumped by a nitrogen laser and using both
fluorescein and rhodamine B. It was dead easy.

Whether any of the commercial Jellos had the right dye in an appropriate
concentration I don’t know.

The one I did was colourless gelatine with rhodamine B or fluorescein
added. Synthetic Jello so to speak. That definitely lased - unsurprisingly
with atrocious beam quality. ;-) I was living in Brazil at the time and
did not have access to the commercial fluorescent Jellos. My guess is they
probably would have lased.

This is probably 100% urban legend, but what I heard as the discovery of the
first dye laser went something like this:

Back in the early 70's or so, remember when everyone had blacklights
and Hedrix posters all over the place? Well, there were some guys that were
working for IBM or some big company that was out in the Boston area somewhere,
and it was late at night and they decided to go out for a drink while they
talked over making a liquid laser. They got into some "blacklight bar" back
then, probably a bit of stuff wisping about in the air, etc., and a noisy
band, etc. But, they being good white shirt and blue tie guys, ordered a round
of Martini's. When the martinin's arrived, the first thing they noticed was
the they were glowing?! This had them a bit stumped as they had been trying a
lot of different dyes and not seeing that much fluorescence with so little
pump source energy like all these blacklights. So, they went to the bar and
asked the bartender to take all the ingredients of a martini and pour them out
into separate shot glasses, well, before it even got poured, they could tell
exactly what it was, it was the gin! So, they bought a fifth of gin and took
it back to their lab and I guess the rest as they say, is history. Or probably
UL, but still, it would be fun to think that's how it happened. I did hear
that from a good source back in the mid 70's while I was still a kid that had
gotten my first HeNe courtesy of a very wealthy uncle who lived in Missasauga
Ontario from a neighbor who had the first laser company in Canada, a fellow
named White if I remember. And they gave me this militarized monster that he
yanked off their line and gave it to me for my 10th birthday. And yes, I still
have it, the uncle passed away on Salt Spring Island BC a few years back, all
those stories and use of gin caught up with him, but having a few millions
tucked away never made his life miserable.. And I even remember when we could
take pictures of the beam and the photo shop would give us the prints for free
as they thought that the red blotch on the print was a mistake they made in
their lab, now that's old. In fact, they even had a monster CO2 laser at the
Ontario Science center that they would blow up stuff with twice a day I think,
I only saw it once, but it was COOOOOOL.

"I have been experimenting with some green fluorescent Perspex pieces
that I obtained a long time ago as samples from a perspex shop. I
found that when I placed them alongside a blue fluoro tube, the ends
lit up *very* brightly. Adding a reflector improved output even
more. Now, I have never been able to coax this stuff into lasing as I
cannot organize appropriate mirrors, however, the ease with which this
material fluoresces make me wonder whether it could be a possible
laser medium. The furthest I got was polishing the ends, wrapping some
flashlamps around the pieces and dumping about 10,000 uF at 350 V into
them. What excited me was that under these conditions, the light
emanating from the ends of these rods is by far the most beautiful and
powerful green light I have *ever* seen (and I've seen a fair bit of
it!). Your thoughts?"

(From: Chris Chagaris (pyro@grolen.com).)

Your idea of building a Perspex laser is not too far-fetched at all. There is
one company that I know of
(A HREF="http://www.dnlabs.com/">DN Labs Laser
Technology) that is manufacturing a high temperature cross-linked,
polymeric solid-state dye laser material. More simply stated: Organic dye
doped plastic laser rods. The Perspex samples that you have may or may not be
doped with an organic dye that would be capable of characteristics as a liquid
organic dye contained in a quartz cell. The mirrors required would not be
terribly specialized and most likely a good quality aluminized high reflector
and a simple partially transmitting aluminized output mirror with about a 70%
reflectance would suffice, if properly aligned. The flashlamp pumping of this
material would be possible if the proper conditions were meant. Organic dyes
require very short and intense pump light pulses to overcome losses due to
molecules that are accumulated in the triplet state. Flashlamp rise-times in
the (hundreds or less) nanoseconds regime are common in practical systems.
This is usually achieved with commercial xenon flashlamps by using a very
high voltage (many times higher than the self-firing voltage) low capacitance
firing circuit with a triggered spark gap in series with the lamp. Your
present low-voltage high capacitance circuit would create very long pump-light
pulses which would not be suitable in such a laser system.